The National Weather Service in Phoenix is pleased to announce that the Yuma WSR-88D Dual-Polarization upgrade will
begin on April 30, 2012. The upgrade will take place between April 30th and approximately May 11th, during
which time the radar data will be unavailable. Neighboring sites, including radars from San Diego, Las Vegas, Tucson, Phoenix, will provide continued coverage during the time of the upgrade. This important technology will greatly expand the amount of data types and radar products available to users. The Phoenix WSR-88D, located at Mesa-Gateway airport, underwent this same upgrade during May of 2011.
On-line Dual-Pol Training Available!.
Until recently, NWS radars transmitted bursts of radio waves, called pulses, in a single, horizontal orientation, or polarization. Upgraded Dual-polarization, or Polarimetric, radars transmit radio waves at a 45-degree angle, allowing both a horizontal and vertical component to be calculated. Being able to analyze data in this manner is expected to result in improvements in the estimation of precipitation rates and amounts, the ability to determine precip types (i.e. rain vs. hail, mixed precipitation types in winter storms), and the identification of non-meteorological returns (insects, dust, etc...).
The radar will measure both the horizontal and vertical dimensions of targets. Since the radar will receive energy from horizontal and vertical pulses, a better estimate of the size, shape, and variety of targets, can be obtained. All these improvements will aid forecasters in the warning decision process, helping the public make better decisions about their safety and protecting their property.
The basic radar products that have been historically available to users are reflectivity (Z), mean radial velocity (V), and spectrum width (SW). These will continue to be available after the upgrade. However, three new products will become available after the upgrade: differential reflectivity (ZDR), correlation coefficient (CC), and specific differential phase (KDP).
Forecasters at WFO Phoenix have already acknowledged the utility of Dual-Pol technology during the 2011 Monsoon season. A strong thunderstorm affected the community of San Carlos, AZ during the afternoon of August 12 and produced a considerable amount of 1" diameter hail. The KIWA radar identified an intense thunderstorm with reflectivities (traditional radar product) over 60 dBZ. However, the radar also detected an area of enhanced Differential Reflectivity (new radar product) indicating an area of vertically oriented meteorological targets (hailstones), as well as an area of decreased Correlation Coefficient (new radar product) indicating a mix of rain and hail.
Click each image for a larger view
|Reflectivity indicating an intense storm near the community of San Carlos.
||Differential Reflectivity indicating large area of vertically oriented "targets" within the storm (red/white shading)
||Correlation Coefficient decreasing to around 0.80 (or lower) indicating a mixture of hail and rain within the storm
Forecasters also put the new data to use during the evening of July 5th, as an enormous dust storm moved from southeast Arizona toward the Phoenix metro area. Traditional radar products indicated that a wind shift was imminent, but dual-pol imagery strongly suggested a large area of dust was moving toward the southeast valley.
Click each image for a larger view
|Reflectivity indicating a large area of 10-20 dBZ returns.
||Correlation Coefficient indicating a large area of non-uniform returns (green and blue shading), highly suggestive of dust
Dual-Polarization Radar Outreach Training has been made available by the NWS Warning Decision Training Branch (WDTB). This training, with separate tracks for meteorologists and non-meteorologists, is targeted at first responders, broadcast meteorologists, other private sector meteorologists, emergency managers and other public stakeholders, and can be accessed from this link.
Traditional WSR-88D radars transmit "pulses" along a horizontal plane (left image). After the Dual-Pol upgrade, the Yuma radar will transmit data in a horizontal AND vertical plane. (right image)